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Flange to web welds calculation of WWF 1
- Thread starter burtonSTR
- Start date
JrStructuralEng
Structural
To add to this question, would you have to design all concrete anchors to take the full shearing force at base (i.e. 60kN/m at base)? or can you stagger the spacing up the wall as the shear force reduces.
JrStructuralEng
Structural
whoops, screwed up my very first reaction calc. Got it now.
I would probably use the following procedure to size the anchors.
1. Size the angle assuming it is reinforcement for the wall.
2. Arbitrarily select some spacing that makes sense (maybe 18").
3. Determine the tension in the angle (at factored load levels) just below each anchor (starting with the second anchor).
4. Use the tension force just below the second anchor to size the first anchor.
5. Use the differential tension force just below the third anchor to size the second anchor.
6. Continue this procedure until you get to the max moment location.
7. Use the largest anchor at all locations.
I just made a quick spreadsheet and this does seem to work out. I was actually questioning myself because I started thinking that the anchor size would actually increase as you get closer to the max moment (that the max shear for the anchors would be at the max moment location), but that's not true. The parabolic shape of the moment diagram (i.e. the x2 term if you develop the equation) helps the diagram shoot up quickly then level off. The max shear in the anchors is still at the first anchor, so I convinced myself that it's completely appropriate (probably more so than trying to use the shear flow formula for this instance).
You can probably quit at step 4 since the first anchor will be the controlling one.
Here is an alternative:
1. Same as above.
2. Choose what size anchor you want to use and determine the shear capacity.
3. Use the formula M/jd (where M is the moment in K-in, and jd is the distance from the centroid of the compression block to the reinforcing - the angle) starting at the bottom of the wall. Set M/jd=<the shear capacity determined in step 2.
4. Determine the location where the inequality in step 3 is true and use that spacing everywhere.
Both of these will get you out of having to figure out which I to use for the wall.
1. Size the angle assuming it is reinforcement for the wall.
2. Arbitrarily select some spacing that makes sense (maybe 18").
3. Determine the tension in the angle (at factored load levels) just below each anchor (starting with the second anchor).
4. Use the tension force just below the second anchor to size the first anchor.
5. Use the differential tension force just below the third anchor to size the second anchor.
6. Continue this procedure until you get to the max moment location.
7. Use the largest anchor at all locations.
I just made a quick spreadsheet and this does seem to work out. I was actually questioning myself because I started thinking that the anchor size would actually increase as you get closer to the max moment (that the max shear for the anchors would be at the max moment location), but that's not true. The parabolic shape of the moment diagram (i.e. the x2 term if you develop the equation) helps the diagram shoot up quickly then level off. The max shear in the anchors is still at the first anchor, so I convinced myself that it's completely appropriate (probably more so than trying to use the shear flow formula for this instance).
You can probably quit at step 4 since the first anchor will be the controlling one.
Here is an alternative:
1. Same as above.
2. Choose what size anchor you want to use and determine the shear capacity.
3. Use the formula M/jd (where M is the moment in K-in, and jd is the distance from the centroid of the compression block to the reinforcing - the angle) starting at the bottom of the wall. Set M/jd=<the shear capacity determined in step 2.
4. Determine the location where the inequality in step 3 is true and use that spacing everywhere.
Both of these will get you out of having to figure out which I to use for the wall.
The angle projects from the wall which does not really help. The rigidity of the angle is not necessary. Since we are considering the steel as external reinforcement, why not use a flat plate anchored to the wall to develop the tension required to resist the applied moment?
Calculate the force in the flat according to your moment diagram. Finally, provide enough anchors to develop that force. above and below the point of maximum moment.
Best regards,
BA
Calculate the force in the flat according to your moment diagram. Finally, provide enough anchors to develop that force. above and below the point of maximum moment.
Best regards,
BA
JrStructuralEng
Structural
StructEIT
A couple questions:
wouldn't you still get similar values by shear flow calc? In essense, it relates the shear to the tension in the section adjacent to the cut? (Doesn't it?) Just curious if you checked your answers against shear flow computation to see if they are close.
At a 48" angle spacing, out of curiosity, what governing anchor 'shear' did you get given your approach? (If you don't mind me asking). My values were pretty high from the shear flow calculation.
A couple questions:
wouldn't you still get similar values by shear flow calc? In essense, it relates the shear to the tension in the section adjacent to the cut? (Doesn't it?) Just curious if you checked your answers against shear flow computation to see if they are close.
At a 48" angle spacing, out of curiosity, what governing anchor 'shear' did you get given your approach? (If you don't mind me asking). My values were pretty high from the shear flow calculation.
JrStructuralEng,
Wf = 45 kN/m
L = 3.0 m
Mf = 0.1283*Wf*L = 17.3 kN-m per m
Tf = Mf/d = 17.3/0.15 = 115 kN per meter
The angle (or strap) has to take a maximum factored tension of 115 kN/m. The anchors must develop that force each side of the maximum bending moment. The spacing must develop the simple span bending moment at all points.
Best regards,
BA
Wf = 45 kN/m
L = 3.0 m
Mf = 0.1283*Wf*L = 17.3 kN-m per m
Tf = Mf/d = 17.3/0.15 = 115 kN per meter
The angle (or strap) has to take a maximum factored tension of 115 kN/m. The anchors must develop that force each side of the maximum bending moment. The spacing must develop the simple span bending moment at all points.
Best regards,
BA
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